FIG. 4 shows an example of a prior art process liquid supplying apparatus for a machine tool. The prior art process liquid supplying apparatus is provided with a tank 19 for collecting a process liquid s, which is supplied to points, for which it is necessary to supply a process liquid, such as a workrest and a workpiece w fixed thereon, a pump 21 for transferring the process liquid s in the tank 19, and process liquid passage means 22a for supplying the process liquid s transferred from the pump 21 to points, for which it is necessary to supply the process liquid, at an optional time.
Cutting chips produced through machining by a machine tool are adhered to or accumulated on a workpiece w and workrest. In order to accurately fix a next workpiece w on the workrest, it is necessary to remove such cutting chips remaining on the workrest when machining of the workpiece w is completed. To solve the above, a process liquid s is consecutively supplied through the process liquid passage means 22a by the pump 21 under adequate pressure at a flow rate over the maximum instantaneous flow rate required, so that cutting chips produced by machining are washed away into the inflow portion of the tank 19. The process liquid s thus supplied may be supplied at frictional points between a workpiece w and a tool as necessary.
In the supply of process liquid s through the process liquid passage means 22a by the above-described prior art pump 21, the discharge capacity of the pump 21 is required to have such a size as can consecutively supply the process liquid at a flow rate over the maximum instantaneous flow rate required to wash away at least cutting chips.
Herein, where it is assumed that the required maximum instantaneous flow rate is Q1, the pressure of process liquid is P0 when it is flown from the terminal of the process liquid passage means 22a, and the pressure loss of process liquid from the outlet of the pump 21 to the terminal of the process liquid passage means 22a is P1, consumption power W1 of the pump 21 is expressed by the following expression: That is,W1=k□Q□(P0+P1)Where k is a constant, and (P0+P1) is discharge pressure of the pump 21.
In an actual example of a machine tool, the above-described Q1 is approximately 200 liters per minute, and the above-described (P0+P1) is approximately 0.3 Mpa. Therefore, the consumption power of the pump becomes comparatively large. There may be cases where the consumption power thereof exceeds approximately 25% of the entire consumption power of a machine tool.
The present invention is considered in view of the above-described situations. It is therefore an object of the invention to provide a method and apparatus for supplying process liquid for a machine tool, by which power required to supply process liquid (coolant and cleaning fluid) can be decreased while maintaining a washing-away capacity of cutting chips produced through machining and a lubrication capacity for points to be lubricated in machining.